1. Field of the invention
The present invention relates, in general, to a method for fabricating a white light emitting diode (LED) which comprises an InGaN thin film as a single active layer and, more particularly, to the phase separation of the thin film upon its growth and the rapid thermal annealing (RTA) of the phase-separated thin film, so as to produce an active single layer capable of emission of intensive white light.
2. Description of the Prior Art
In order to emit white light, there are needed all the three primary colors of light. The most fundamental method to emit white light with LEDs is to combine three red, green and blue LEDs. This enables the emission of a white color comfortable to the human eyes in addition to being very efficient because the individual short wave LEDs can be independently controlled. This method, however, suffers from the disadvantages of being unfavorable economically and productively and being extremely limited in application range.
S. Nakamura reported a white LED in which a luminescent material such as phosphine is applied for a blue or UV short wave LED ("The Blue Laser Diode" pp. 216-219, 1997). This LED is operated in such a manner that the light with an energy sufficient to cause excitation, emit-ted from the blue or UV short wavelength LED, excites the luminescent material to effect light in a yellow wavelength range, thus emitting white light on the whole. This technique has been extensively studied in Japan and is now on the brink of commercialization. The recruitment of the luminescent material enjoys ease in fabricating the white LED. However, this technique is significantly disadvantageous in that the diode is poor in luminescent efficiency because the light coming from the short wavelength LED is partially absorbed in the luminescent material.
As an alternative to avoid the self-absorption, an LED is disclosed in Appl., Phys. Lett., 70, 2664, 1997, which uses a semiconducting conjugated polymer, instead of a luminescent material, in cooperation with a blue short wavelength LED. The semiconducting conjugated polymer shows an energy gap of 1-3 eV and has energy absorption edges which are separated sufficiently from the wavelength of the light emitted, so that its self light absorption is minimal. This technique is high in energy conversion efficiency and has such an advantage that the white color can be tunably expressed by using appropriate polymers and controlling their thickness. As in the luminescent material technique, the short wavelength diode is required to be additionally processed. Other disadvantages of this technique are that the white LED fabricated is low in luminescent efficiency and its use environment is severely restrained by the polymer employed.
Accordingly, the ultimately demanded device is a diode which directly emits white light from a single chip, just like the short wavelength LED, without any luminescent materials or semiconducting conjugated polymer. In fact, a single chip white LED which has a structure of metal-insulator-n type GaN was reported in Tech. Phys. Lett., 22, 441, 1996, by Drizhuk et al. According to the report, when an active insulating layer (I-region) which shows a high specific resistance at low temperatures, is grown on an n-type GaN layer, zinc (Zn) is doped in one layer while zinc (Zn) and oxygen (O) are doped in the other layer, so as to cause white light emission. Although enjoying an advantage of producing a white color without the aid of luminescent materials or polymers, this technique suffers from a significant disadvantage in that, since the white light is emitted from the defect level which is formed by the dopants in the I-region grown at low temperatures, the luminescent efficiency is too low to produce an economical benefit.